Untangling the reaction dynamics of the silylidyne radical (SiH; X²Π) with acetylene (C₂H₂; X¹Σ_g⁺)

The chemical reaction dynamics of silylidyne (SiH; X²Π) with acetylene (C₂H₂; X¹Σ_g⁺) were studied exploiting the crossed molecular beam approach, and compared with previous studies on D1-silylidyne with acetylene. The reaction is initiated by a barrierless addition of silylidyne to one or both carbons of acetylene leading to 1-sila-1-propene-1,3-diylidene and/or the cyclic 1-silacyclopropenyl with the former isomerizing to the latter. 1-Silacyclopropenyl eventually loses atomic hydrogen yielding silacyclopropenylidene (c-SiC₂H₂) in an overall exoergic reaction (experiment: -14.7 ± 8.5 kJ mol^-1; theory: -13 ± 3 kJ mol^-1). The enthalpy of formation for silacyclopropenylidene is determined to be 421.4 ± 9.3 kJ mol^-1.